Snails can make complex decisions ‘with only two brain cells’

Snails are not known for their quick thinking but can make complex decisions using just two brain cells, scientists have learned.

One cell tells the mollusc if it is hungry or not while the other lets it know when food is present.

The discovery, made using electrodes to measure activity in the brains of freshwater snails searching for lettuce, could help engineers design more efficient robots.

Lead researcher Professor George Kemenes, from the University of Sussex, said: “What goes on in our brains when we make complex behavioural decisions and carry them out is poorly understood.

“Our study reveals for the first time how just two neurons can create a mechanism in an animal’s brain which drives and optimises complex decision-making tasks.

“It also shows how this system helps to manage how much energy they use once they have made a decision.

“Our findings can help scientists to identify other core neuronal systems which underlie similar decision-making processes.

“This will eventually help us design the ‘brains’ of robots based on the principle of using the fewest possible components necessary to perform complex tasks.”

In order to test the snail’s decision-making, the researchers hooked up electrodes to monitor changes in activity in its brain, which picked up on spikes in the activity of individual neurons.

They found that the two cells – a controller and a motivator – fed back to each other to make the decision. If food is present, the controller lets the animal know, and if the motivator says it is hungry, then the snail will nibble away.

But if food is not present, then the circuit can dial itself down, saving energy.

Seeking out food is a fundamental survival skill for animals and an example of goal-directed behaviour.

During such goal-directed decision making, an animal must integrate information about both its external environment and internal state while using as little energy as possible.

Professor Kemenes said: ‘Our findings can help scientists to identify other core neuronal systems which underlie similar decision making processes.

“This will eventually help us design the ‘brains’ of robots based on the principle of using the fewest possible components necessary to perform complex tasks.”